Free volume in microcanonical multifragmentation

The microcanonical multifragmentation model from [Al. H. Raduta and Ad. R. Raduta, Phys. Rev. C 55, 1344 (1997); 56, 2059 (1997); 59, 323 (1999)] is used for evaluating the free volume corresponding to the primary break-up in two freeze-out hypotheses: $\rho=\rho_0/3$ (SMM like) and $\rho=\rho_0/6.59$ (microcanonical like) for three source nuclei: (70,32), (130,54), (190,79). Plateau-like regions and even backbendings of the free-volume versus excitation energy are evidenced (for all cases except (130,54) and (190,79) at constant nuclear temperature. Important differences from the free volume curves employed in SMM are pointed out indicating some physical inconsistencies of the usual parametrization of the above-mentioned model